Sealing of alkali sensitive films and pellicles



Nov. 7, 1961 D. T. MILNE SEALING OF ALKALI SENSITIVE FILM-S AND PELLICLES Filed. Nov. 1, 1956 United States Patent 3,007,832 SEALING F ALKALI SENSITIVE FILMS AND PELLICLES David T. Milne, Fredericksburg, Va., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware Filed Nov. 1, 1956, Ser. No. 619,750 9 Claims. (Cl.156-80) surfaces, it is generally desirable, because of the strength of the alkali solution used, to neutralize the alkali after such sealing so as to strengthen the ness, and prevent contamination of other goods thatmay be brought into contact with other areas of the joints. The presence of strong alkali, if not neutralized, is particularly objectionable in the wrapping of meat. Furthermore, if, for example, casings having joints containing appreciable alkali are stored in a flattened condition, the alkali will leach into adjacent casings brought into contact with the joined portions to cause cohesion. Neutralization of the alkali may be accomplished by acid materials, such as dilute acetic acid or vinegar, but unless the casings are to be usedirnmediately, .any' acid must be flushed from the casings or eventually it. will embrittle and weaken the alkali-soluble material. n It is a primary object of the present invention to pro vi'de a process for sealing alkali-soluble sheet materials which may be accomplished with such a low concentration of alkali as to render neutralization unnecessary under the usual conditions of use of such sheets or films. Another object is to provide a process in which a high degree of adhesion is obtained practically instantaneously as the portions of the material brought together. Still another object is to provide a process in which a simple dilute alkaline solution which does not contain any other ingredient may be used. Other objects, features and advantages will become apparent from the following description of the, invention and the drawing relating thereto in which:

FIGURE 1 is a side elevation partly in section of a form of apparatus with which theinvention may be practiced;

FIGURE 2 is a plan view of the form of apparatus shown in FIGURE 1;

FIGURE 3 is a sectional view of the form of apparatus shown in FIGURE 1, the section being taken along line 3, 3 in FIGURE 1; g

' FIGURE 4 is a fragmentary view in section, taken along line IV- IV of FIGURE 2, of adjacent portions of tube-forming equipment; and n FIGURE 5 is'a fragmentary plan view of a hollow edge portion of a tube former shown in FIGURE 4.

In brief, the invention comprises providing an alkalijoint, eliminate tackiforming the joint are wholly or partly therein for conventional plasticizers. In many instances the alkaline solution may be applied in restricted amounts to eliminate a drying operation following the sealing operation.

As the drawing suggests, the method of sealing taught herein is readily adapted to the manufacturing of stuffed meat products since the method is particularly useful in forming tubular 'casings in which edged portions of a sheet are continuously brought into overlapping relationship, moistened with the dilute alkaline solution and sealed together to form a tube. As the sealing is instantaneous, such a casing may be stuffed and packed with meat within the same apparatus.

However, unstuflied casings which are completely dry and are prepared in a flattened condition for shipment to a user, or for storage for an indefinite period of time, may be prepared by an apparatus such as: disclosed in my application, Serial No. 460,571, filed October 6, 1954, now Patent No. 2,845,357. Portions of the apparatus disclosed in the said application are provided for applying a neutralizer and would normally not be used in forming casings in accordance with the present invention. However, if a neutralizer is used, it can be applied by the neutralizer-applicator portion of the apparatus in greatly reduced quantity or concentration as compared to that required for sealing a cellulosic material containing no urea.

The seamed or jointed articles of thin gauge materials produced in accordance with this invention comprise alkali-soluble water-insoluble cellulosic materials, such as a lower alkyl hydroxy-alkyl, orcarboxyalkyl ether of celulos'e; preferredspecific materials being methyl, ethyl, hydroxyethyl, and carboxymethyl ethers of cellulose, mixed cellulose ethers in this class; and also sheets derived from cellulose ether-xanthates, cellulose xant-hoethers, cellulose thiourethanes, and cellulose xanthofatty acids. Such cellulosic materials may be used in combination with a flexible base such as a porous paper. A preferred material, for example, that may be used in practicing the present invention is a thin porous paper thoroughly impregnated with an alka '-soluble cellulosic material, such as hydroxyethyl cellulose. Such a material is rendered immediately tacky by alkaline solution and in a condition ,for making joints by an alkaline solution of greater than 6 percent alkali. However, joints may be made in a wrapping material constituted of any one or more of these cellulosic materials soluble sheet or film of cellulosic material'impregnated with urea whereupon a oint may be obtained between any desired surfaces of the material by simply wetting such surfaces with a solution having an alkaline concentration of from approximately 1' to 6 percent, pressing the surfaces together and drying them. In optional practice of the invention, alkaline solutions of very low con centrations may be more efliciently usedby'chilling the materials which form the joint. Theurea may also be used as a plasticizer for the sheet or film and substituted through the use of tackifying solutions containing less than 6 percent of an alkali when such material contains a small percentage of urea. The tackifying solution or adhesive used in sealing edges or portions of urea-impregnated alkali-soluble material may be a solution of sodium or potassium hydroxide or other strong base of less than 6 percentconcentration which may contain in addition, but not necessarily, one of the alkali-soluble cellulosic materials, preferably that material comprising the members to be joined. In a preferred manner of practicing the invention, the amount of tackifying solution applied to the members to be joined is carefully controlled so as not to cause an excess of the solution to be squeezed from the joint and thus make necessary the use of a neutralizing medium and/ or a drying operation. The amount of alkaline solution applied, for example, may be satisa factorily controlled by feeding it through a wick or other distributor held in contact with the surfaces to be joined, and applying thereto merely enough solution to moisten such surfaces.

I After the portions of the sheet or film have been joined asthe result of adhesion developed by the tackifying solution, they are preferably subjected to pressure to assure good union of the joined portions. If the joints tend to become brittle after thorough drying, as for exr 3 ample, in the production, storage, and distribution in commerce of empty casings, a small amount of a plasticizer the plasticizing baths and of the film after drying are asfollows:

such as one of the polyhydric alcohols may be incorpo- Table A rated in the tackifying solution to provide sufiicient plastlollatwn Wlthm the 1m Example 1 II III 1V V Although urea alone may be used as a plasticizer for the sheet materials treated in accordance with this inven- Composition of Plasticizing Bath: tron, it as normally moreeconormcal to use urea in that g gg g -3 I @g 2-3 amount which results in good joints in combination with 33% 'SBHi'ufii 2' e'th1' antenna that amount of plasticizer which, together with the urea,. $g- 9 0 results in good softening of the film or sheet. Although rea ..percent.. 0 o 15.1 16.0 10.0 uream y be u ed-in n m n a low as 1 p rcent of g gg ng"; g &3 813 g t3 the dry weight of the to noticeably reduce the con- Gellulosic Material .do-.- 70.8, .71. a. 70.4 can 74.6 centration. of required in the tackifying, solution,

Table. B

COMPARISON OF STRENGTHS IN JOINTS A'I 24 0.

Example I n In iv v' NaOH in Tacklfying'solution:

2% Very-Poor... Very Poor..- Poor Poor Poor.

4% Poor P0or Extra Good..- Extra Good.

6%.... Goo Good Excellent-m..- Excellent.

8% Excellent Excellent... do Do.

Explanation of Terms in Table B ExcellentTears the film in other place than seal. Extra Good-Tightseal, slight tendency to tear the film rather than the seal.

Good-Medium sea for efiective use of the invention, concentrations of at least3 percent are desired, andurea may be incorporated in the film or sheet to an amount up to'as In ch as percent of its dry weight for plasticization and sealing I mercial packaging material willcontain a total of 151 to 25. percent of a plasticizer (based on thedry weight of the film). 0t, this amount, urea, may amount to 3 to 20 percent with, the remainder, consisting of another plasticizer to provide satisfactory scaling of. joints as required by invention.

The following examples illustrate joints made in accordance with the invention, as well as joints made with materials which. do not containurea so that comparisons may be drawn which demonstrate the effectiveness of the invention. as claimedherein,

EXAMPLES ITO V were prepared from a solution comprising 715 percent alkali-soluble water-insoluble hydroxyethyl' cellulose, 7.5 percent sodium hydroxide and 85 percent water by casting this solution on a polyethylene helt'by means of a reverse roll coater. The hydroxyethyl cellulose was a low etherified' type in which ethylene oxide units were attached to the cellulose in a ratio of about" one to 4' or 6' glucose units, i.e., a substitution factor of about 0.2. The filml was coagulated in a solution comprising'll to 15 percent sulfuric acid and 24.5 to 26.3 percentso diurn, sulfate at 40 C. Following coagulation, film was washedin water; at 75 C. and plasticized at 75 C. in plasticizing baths, the ingredients of which are listed in Table A below. After plasticizing, the-filmwas dried on heated rollers at 75 C. The composition of In the above examples commercially satisfiactory seals were obtainable with films. having a urea-content of! 10. percent or higher with tackifying, solutions as low. as 3 or 4 percent concentration of alkali. On the other hand, the film samples of I and II contained no urea and pro ducedpoor seals when the joints were made when using a. tackifying solution of, 4 percent alkali; commercially acceptable joints were obtained. only when the. alkaliconcentration was increased to above 6. percent- Theabove examples,. while illustrative of the relative effectiveness of seals made in. an alkalisoluble cellulosic material. containing some urea in the one case and. no urea in the other case, do. not embody conditions. which are conduciveto mosteconomical use of alkali and urea. For example, the. seals of these examples were made at roomtemperature. The. concentration of the. alkali solution used for joiningurca-containing hyd'roxyethyl cell'us lose may be readily reduced to 1 percent if sufficiently low temperatures are employed, e.g., a temperature of 10 C. or lower. Equipment for obtaining cold seals" is, described hereinafiter. The chilling may be accomplished by applying refrigeration to the alkali. solution in its reservoir, by chilling the surfaces (wet. or dry) justbefore. the joining, thereof, and/or by chilling the joint immediately afiter its formation; before the water of the alkali solutionhas evaporated or. has opportunity to bewicked in any substantial.- extent away from the surfaces wetted by solution. The above examples were conducted with hydroxy ethyl cellulose offilm grade which. is made with relatively low etherization in order to obtain low sensitivity to water. However, thesealing of such films may be implemented. at very low alkali concentrations in practicing the. present invention by increasing. the. extent of substitution, short of water solubility,.of ethylene oxide units on the glucose units of the. cellulose in the original prepaaration of the hydroxyethyl cellulose, e.g., to any value up to. 0.4 ethylene oxide units. substitutionper glucose unit. Hydroxyethyl cellulose up to this degree of etheriZation retains water insolubility. Within this range of etherization, sealing solutions having no more than 1 percent alkali arepracticable.

Referring to FIGURES l, 2 and '3 of the drawing in which is shown a form of apparatus with which this invention may be practiced, reference character indicates a nozzle having a threaded end 11 adapted to screw on the outlet pipe '12 ,ofa conventional sausage meat container 9 to replace the nozzle conventionally used thereon. Since the meat in the container 9 is customarily "placed under hydraulic pressure, the valve 8 is adapted and arranged to control the flow of the meat through the nozzle in the usual manner. On the underside of the nozzle 10, there is mounted a bracket 13 adapted to support a roll of casing-forming, urea-containing hydrophilic sheet material 14. On each side of the nozzle there is mounted a tube-former 15 which encircles the nozzle and is arranged to shape the sheet material into a tubing 16 about the nozzle. There is also mounted on the nozzle 10 a liquid reservoir 27, for an alkaline solution, having a lid 7 and means such as a wick 17 for applying this solution to at least one of the overlapping surfaces of the hydrophilic sheet to form a longitudinal seam 18. An arcuate roller or shoe 19 is supported on a forked spring 20 and is positioned to apply pressure to the seam 18.

It is desirable to feed the sheet material in such a position that the center and the edges of the sheet are displaced an equal distance from the longitudinal axis of the nozzle. This is done, as shown in FIGURES 1 and 2, by

forming the nozzle with a reverse curve at the end adjacent to the meat container, and there is provided a guide roller 28 which is so positioned that its upper surface lies in the same plane with the axis of the free end of the nozzle 10. Thus, when the roll of sheet material is passed over this roller, it is roughly at the same level as the center of the nozzle and is suitably positioned for the formation of the tubing. It is to be understood that the nozzle may be reversed so that the roll 14 is positioned on the top side of the nozzle while the alkaline solution reservoir is on the underside, in which case the seam is formed on the underside of the nozzle. Instead of using a wick 17, an equivalent means such as a roller or disk which dips into the alkaline solution reservoir and then contacts an edge of the sheet material may be employed, and such alterna tive means is particularly adapted when the nozzle is reversed.

FIGURE 3 is a cross-section of the nozzle shown in FIGURE 1 and taken along the line 33 thereof, in which is illustrated the nozzle 10, and the sheet material 16 surrounding the nozzle and overlapping at the top to form the seam 18. There is also shown a roller or shoe 19 that presses the overlapping edges of the seam 18 against the nozzle 10. The roller 19, as shown, is made hollow whereby it may be chilled by means, such as refrigerated brine circulated therethrough, to implement the sealing operation. A turn-buckle screw clamp 29 holds refrigerant line connectors in place over the ends of coaxial hollow shafts of the roller 19. I

In forming a cold" seal, further chilling of the materials from which the seal is formed may be accomplished by providing a cooling coil 30 inside the alkaline solution reservoir having extremities connected with a refrigerated brine supply and return lines 31 and 32 respectively. Referring to FIGURES 1, 2, 4, and 5 of the drawing, the under hollow edge portion 34 of the tube former 15 (in overlapping relation with the outer edge portion 35) has a chamber 36. The edge portion 34 has passageways through its walls to the chamber as provided at 37 and 38 for passing a refrigerant into and out of the chamber.

In the operation of this invention, the sheet material 14 is passed over the guide roller 28 through the forming means 15 and shaped thereby into a continuous tubing 16 having overlapping edges to form a seam 18. Between the overlapping edges there is applied an alkaline aqueous solution from the wick '17, and the edges are then pressed together by means of the chilled roller or shoe 19 of 6 arcuate profile bearing on the upper surface of the nozzle. After the seamed tub g 16 passes beyond the end of the nozzle 10, the tubing is tied and then may be filled with sausage meat. 'The flow 'ofthe sausage meat is controlled by means of the 'valve 8 and if desired, the stuffed casing is twisted at intervals to provide sausage links.

Various changesand modificationsrmay be made in practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

I claim:

l. A process for the production of tubular casings comprising guiding a flexible sheet of a cellulosic material longitudinally to a forming position, said sheet being prepared from a starting material containing as an essential component a hydroxyalkyl cellulose ether and said sheet being plasticized with a minor amount of urea, continuously shaping the sheet into a tubular form with the longitudinal edges overlapped, and sealing the overlapped edges with an alkaline solution so as to form a sealed tubular casing, the urea content of the sheet coacting with the alkaline sealing solution to accelerate the sealing process.

2. Process of claim -1 wherein the sheet is formed by the coagulation of a cellulose ether-xanthate solution, the cellulose ether portion being hydroxyethyl cellulose.

3. Process of claim 1 wherein the urea is present in the sheet in an amount of 3-30% and the casing is sealed at a temperature of 10 C. or lower using an alkali concentration of not more than 1% by weight in the sealing solution.

4. In a process of sealing together portions of a flexible sheet comprising a water-insoluble, alkali-soluble cellulosic derivative by wetting areas of said sheet to be joined with a solution containing alkali and pressing said areas together while wet, the improvement comprising impregnating said sheet with from about 3 to 30% of urea based on the dry weight of said sheet prior to the wetting of areas of said sheet with said solution of alkali.

5. The improved process of claim 4 further characteiized in that said solution contains from about 1 to 6% al ali.

6. The improved process of claim 5 further characterized in that prior to wetting with said alkaline solution a wetting agent and a polyhydric alcoholic plasticizer are applied to said sheet.

7. In a process as defined in claim 6 wherein the polyhydric alcohol is a compound of a group consisting of glycen'ne, ethylene glycol, diethylene glycol, sorbitol.

8. In a process as defined in claim 5, wetting the areas to be joined with an alkali solution having an alkali concentration no greater than about 1 percent, and chilling said areas wetted before the water of solution has substantially left said areas.

9. In a process of sealing together portions of a flexible sheet comprising a water-insoluble, alkali-soluble cellulosic derivative by wetting areas of said sheet to be joined with a solution containing alkali and pressing said areas together while still wet, the improvement comprising impregnating said sheet prior to wetting with said alkaline solution with at least 1.5% urea based on the dry weight of said sheet.

References Cited in the file of this patent UNITED STATES PATENTS 1,951,474 Eastman Mar. 20, 1934 2,106,296 Dreyfus Jan. 25, 1938 2,288,413 Morgan June 30, 1942 2,339,562 Eustis Jan. 18, 1944 2,477,768 Remer Aug. 2, 1949 2,546,575 Woodling Mar. 27, 1951 (Other references on following page) Harder-,et'al Dec,. .111, 1,956

:8 V -:FORE IG,N PATENTS 599,739 --('3reat'B1"-i-tain -0ct. *6, 1 948 QZIH'ER REFERENCES 7 'Apifllcai ions 'anfi'Uses of Chemical Compounds and Similar Materials, 1101. 1, Urea, page 629. 

1. A PROCESS FOR THE PRODUCTION OF TUBULAR CASINGS COMPRISING GUIDING A FLEXIBLE SHEET OF A CELLULOSIC MATERIAL LONGITUDINALLY TO A FORMING POSITION, SAID SHEET BEING PREPARED FROM A STARTING MATERIAL CONTAINING AS AN ESSENTIAL COMPONENT A HYDROXYALKYL CELLULOSE ETHER AND SAID SHEET BEING PLASTICIZED WITH A MINOR AMOUNT OF UREA, CONTINUOUSLY SHAPING THE SHEET INTO A TUBULAR FORM WITH THE LONGITUDINAL EDGES OVERLAPPED, AND SEALING THE OVERLAPPED EDGES WITH AN ALKALINE SOLUTION SO AS TO FORM A SEALED TUBULAR CASING, THE UREA CONTENT OF THE SHEET COACTING WITH THE ALKALINE SEALING SOLUTION TO ACCELERATE THE SEALING PROCESS. 